1. Field of the Invention
The present invention relates, in general, to printed circuit boards and, more particularly, to a printed circuit board, which has a wiring structure enabling the number of memory modules mounted on the printed circuit board to be easily expanded.
2. Description of the Related Art
Generally, a memory device is used to temporarily or permanently store data or instructions used in computer systems, such as a personal computer (PC), a workstation or a server. Dynamic Random Access Memory (DRAM), Static RAM (SRAM), Rambus DRAM, and Extreme Date Rate (XDR) DRAM can be referred as a representative memory device. Such a memory device is actually applied to a computer system in the form of a module (hereinafter, referred to as a ‘memory module’). That is, a memory module, in which a plurality of memory devices is mounted, is connected to and is installed in a panel (for example, a motherboard provided in a PC), with the memory module being inserted into a slot on a Printed Circuit Board (PCB).
Meanwhile, a processor (typical chipset) and a memory module are connected to each other through various wiring schemes. In this case, wiring is implemented in a point-to-point manner. In point-to-point wiring, data or a signal generated by the processor is actually effectively provided only to a single memory device mounted in the memory module.
FIG. 1 is a diagram of a memory system including a conventional PCB 100, which shows the structure existing before memory modules are inserted into slots. The PCB 100 of FIG. 1 includes two slots 110 and 120, into which memory modules, each having a plurality of memory devices mounted therein, can be inserted. In FIG. 1, wires 131 to 133 transmit data. Further, the controller terminals 141 of the wires 131 and 132 are connected to a processor 1 and are capable of transmitting or receiving data to or from the processor 1. The module terminals 142 and 143 of the wires 131 and 133 are electrically connected to a memory module inserted into the first slot 110, and are capable of transmitting or receiving data to or from the memory module. Further, the module terminals 144 and 145 of the wires 132 and 133 are electrically connected to a memory module inserted into the second slot 120 and are capable of transmitting or receiving data to from the memory module. In FIG. 1, wires 134 and 135 transmit instruction signals. The instruction signals received by the connection terminals 146 of the processor 1 are provided to the connection terminals 147 and 148 of the slots 110 and 120 through the wires 134 and 135, respectively. Further, the driving of memory devices mounted in the memory modules is controlled by the provided instruction signals.
However, in the conventional PCB 100, individual wires 133 are not connected to the controller terminals, which can be directly connected to the processor 1. In the conventional PCB 100, when a memory module is inserted only into the first slot 110, the module terminals 143 of the first slot 110 are not electrically connected to the processor 1.
Therefore, in the conventional PCB 100, as shown in FIG. 2, when only a single memory module is actually used to store valid data, the insertion of a dummy module 170 into the second slot 120 is required. Through the connecting wires 171 of the dummy module 170, the module terminals 144 of wires 132 are electrically connected to the module terminals 145 of wires 133. Furthermore, the memory devices 161 of a memory module 160 inserted into the first slot 110 can transmit or receive data through DQ pads 161b connected to module terminals 143.
Meanwhile, in order to expand the number of memory modules, two memory modules 160 and 180 are inserted into first and second slots 110 and 120, respectively, as shown in FIG. 3. In this case, data is not input/output through DQ pads 161b and 181b connected to the module terminals 143 and 145 of the wires 133.
However, in the conventional PCB 100, only a maximum of two memory modules can be mounted. Therefore, the conventional PCB 100 is problematic in that it is difficult to expand the number of memory modules.